Various electronic devices contain components that are sensitive to voltage surges, for example from a power supply. Typically, surge protectors are employed to ensure that the voltage supplied to a protected electronic device does not exceed a clamping voltage. For certain electronic devices, it may be advantageous to integrate a surge protector with the device to provide protection where another surge protector is not utilized, for example when the electronic device is coupled to a wall socket via a charger. In these instances, it is important that the surge protector have a small form factor so that the size of the electronic device is not unduly increased.
Conventional devices that provide such voltage clamping or protection against surge events include transient voltage suppression (TVS) diodes and voltage regulators realized through analog circuitry. TVS diodes possess a clamping voltage that varies with the current being sunk by the diode; that is, the clamping point for the TVS diode tends to be higher than the trigger voltage for that diode. The slope between the trigger point and the clamping point on a current-voltage plot is referred to as dynamic resistance. It is desirable to reduce dynamic resistance of a clamping device to provide precision with respect to the clamping voltage of that device, regardless of current levels. Analog circuit-based voltage regulators typically provide precise control over clamping voltage, but react (or “turn on”) slowly to a TVS event, and thus are likely to fail in the event of a fast edge TVS event. Further, these voltage regulators add a series resistance, which is disadvantageous where the regulation is applied to a power supply input of a device, for example. For these reasons, neither TVS diodes nor analog circuit-based voltage regulators are ideal for TVS clamp applications.